Thoracic outlet syndrome (TOS) is an umbrella term for conditions involving the compression of neurovascular structures (e.g., the brachial plexus or the subclavian artery or vein) as they pass from the lower neck to the armpit. Causes include trauma, tumors, or the presence of a cervical rib. Neurogenic TOS is the most common type and involves the compression of the brachial plexus, leading to neck pain and numbness and tingling in the fingers. Arterial TOS involves compression of the subclavian artery and presents with pain, pallor, coldness, and pulselessness in the affected arm, especially during overhead activities. Venous TOS results in pain, cyanosis, and swelling of the arm. Imaging techniques such as duplex sonography, X-ray, MRI, or electrodiagnostic testing are used to detect the cause of TOS. Mild symptoms should be treated with pain medication and physical therapy. Surgical resection of the causal structures might become necessary in the case of progressive neurologic dysfunction or acute vascular insufficiency.
Compression of subclavian vessels and the lower trunk of the brachial plexus (mainly occurs within the scalene triangle) due to:
- Physical trauma (e.g. hyperextension neck injuries)
- Repetitive motion of the abducted and externally rotated shoulder; (e.g., tennis, baseball, swimming, repetitive throwing, carrying heavy objects overhead)
- Structural abnormalities
Clinical features of TOS depend on the anatomic structure affected by compression and are more pronounced during and after overhead activity.
- Compression of parts of the brachial plexus (95% of cases) 
- Compression of the subclavian vein (up to 3% of cases) 
- Compression of the subclavian artery (< 1% of cases) 
Swelling and venous distention in the arm may be a sign of venous thrombosis of the arm.
- Adson test: a provocation test that is used to reproduce symptoms of TOS
- Wright test: a provocation test used to reproduce paresthesia and changes in the radial pulse by performing the following maneuvers
- Roos stress test: a provocation test used to reproduce symptoms of TOS
- Other: depend on suspected underlying pathology
- In mild cases
- Thoracic outlet decompression surgery: in cases of acute vascular insufficiency or progressive neurologic dysfunction or if conservative treatment fails